1. Field of the Invention
This invention relates to an ink jet recording apparatus which performs recording by ejecting ink to a recording medium and, more particularly, to a recording medium transport mechanism capable of preventing, for a long period of time, re-transfer of ink to the recording medium caused by a rotary discharge member for discharging the recording medium after recording and a following rotary member which contacts the rotary discharge member, and also to an ink jet recording apparatus using the recording medium transport mechanism.
2. Description of the Related Art
Conventionally, recording apparatuses such as printers, copying machines and facsimile machines are arranged so that an energy generating meter of a recording head is driven in accordance with image information transmitted to the apparatus to record an image formed of dot patterns on a recording sheet such as a sheet of paper or a thin plastic plate. Recording apparatuses using an ink jet system, i.e., ink jet recording apparatuses, among such recording apparatuses, perform recording by ejecting ink from a recording head onto a recording member, and are advantageous because they can easily be designed so as to be smaller in size, can record an image with accuracy at a high speed, can record an image on plain paper without any special pretreatment, can be used at a small running cost, can operate with reduced noise since they are of a non-impact type, and can easily be designed to record a multi-color image by using multiple color inks. In particular, it is possible to further increase the recording speed of line type ink jet recording apparatuses having a line type recording head in which a multiplicity of ink ejection outlets are arranged in the direction of the recording sheet width.
However, since ink jet recording apparatuses perform recording by ejecting ink to a recording member, ink on a recording member cannot dry easily in the case of high-density recording or recording under high-temperature and high-humidity conditions. In such a situation, a roller on the recording surface side in a pair of discharge rollers positioned downstream of a recording section may be contaminated with ink, and the ink may be again transferred to the recording medium to contaminate the recording surface. A method for solving this method, such as that described in Japanese Patent Publication No. 51999/1986 or Japanese Laid-Open Patent application No. 142247/1991, is known in which a cleaner member is brought into contact with the roller on the recording surface side in a pair of discharge rollers positioned downstream of a recording section to remove ink attached to the roller surface, whereby re-transfer of ink to the recording medium is prevented. In particular, in conventional ink jet recording apparatuses, it is necessary to minimize such transfer to the roller in order to limit the reduction in density on the recording surface. Therefore, an arrangement has been adopted in which spur like rollers having a smaller area of contact with the recording surface are used and extreme ends of their teeth portions are cleaned by a cleaner.
However, an effect of completely removing ink attached to the tooth ends of a spur-like roller has not been attained even by providing a cleaner in contact with the tooth ends for the purpose of preventing re-transfer of ink to the recording surface. If this method is used, retransfer to the recording surface of the recording member cannot be recognized with the human eye, but a very small amount of ink is attached to the discharge roller for discharging the recording member after recording when the discharge roller contacts the tooth ends of the spur-like roller after discharging. Accordingly, with the increase in the number of recording sheets, the amount of ink attached to the discharge roller becomes larger, and there is a risk of the surface of the recording member on the discharge roller side (the reverse surface opposite from the recording surface) being seriously contaminated by the attached ink. In particular, in the case of an overhead projector (OHP) sheet, a contamination on the reverse surface can be recognized as definitely as a contamination on the obverse surface when projected, and it is possible that the durability of the apparatus, i.e., the number of sheets used for recording by continuously operating the apparatus without maintenance, must be limited. If an ink having improved water fastness is used, the durability may be considerably reduced because such an ink has high adhesion and fastening properties in comparison with ordinary ink.